What issues can arise when seeking a 30-day extension at the Samut Prakan Immigration office?

The border is just south of Bearing BTS station on Sukhumvit. If you're north of this you have to go to the other side of Bangkok

Where do you live? If your address is in Bangkok you cannot go to the Samut Prakan immigration office. If your address is in Bangkok you can only go to the IT Square Laksi immigration office if you entered without a visa and got a 30-day visa exempt stamp.

If your address is in Samut Prakan then the ONLY place you can go for an extension is the Samut Prakan immigration office.

You go to the one that serves where your TM30 is registered, you cannot choose. BTW - If you entered on an actual Tourist Visa which you paid before you flew into Thailand and were stamped for 60 days, you are going to go to Chaengwattana Immigration office, Government Complex Building B.

If you entered Thailand without purchasing a visa prior to your travel to Thailand, you are going to go to IT Square Laksi Plaza temporary office, just next to Lak Si station on SRT Dark Red Line.

With a Tourist Visa (60 days entry stamp) you go to Chaengwattana - counter J, with Visa Exempt (30 days entry stamp) you go to IT Square Laksi Plaza 3rd floor, counter K.